This invention relates to a photo-polymerizable composition and, more particularly, to a rapidly photocurable resin composition useful for dental restorative and tooth coating purposes.
Adhesive compositions that harden when exposed to ultraviolet light have been used for dental restorative purposes for quite some time. In particular, various acrylic resins have been used as binders in these compositions. Compounds disclosed in U.S. Pat. Nos. 3,066,112, 3,179,623 and 3,194,784 are typical of these acrylic resins. Especially noteworthy is a compound having the formula ##STR1## which is glycidyl methacrylate derivative of bisphenol-A, sometimes referred to as bisphenol-A-bis-(3-methacrylato-2-hydroxypropyl) ether or, more conveniently, as BIS-GMA.
The successful use of BIS-GMA in the adhesive sealing of pits and fissures for caries prevention with use of ultraviolet light has been described by Buonocore in J. Amer. Dent. Assn. 80 (2), 324-328 (1970). The major components of the adhesive composition were stated to be three parts by weight of the BIS-GMA and one part by weight of methyl methacrylate monomer. The adhesive, to which 2% benzoyl methyl ether was added just before used, was painted on acid-conditioned enamel surfaces and exposed to ultraviolet light for a few seconds to induce polymerization hardening.
In the foregoing BIS-GMA dental restorative compositions, the low molecular weight methyl methacrylte serves essentially as a reactive extender or diluent to reduce the viscosity of the compositions, as noted in U.S. Pat. Nos. 3,066,122, 3,539,533 and 3,709,866, whereby they can be conveniently used in dental applications. The benzoyl methyl ether is employed in these compositions as a photosensitizer. This is a substance which absorbs actinic radiation so as to produce free radicals which initiate polymerization and cross-linking reactions.
Another substance typically used in the dental restorative compositions is benzoyl peroxide or a similar such compound which serves as a free radical initiator or catalyst for the polymerization reaction.
While the foregoing dental restorative compositions are useful, a chronic problem which arises in practice is inhibition caused by the presence of oxygen. Because of this inhibition by oxygen, the desired complete hardening of the resin to the surface to which it is applied is not obtained and, instead, a tacky surface is produced.